Solve for $f$. $0.3=0.5f-0.7 $
Let's add and then divide to get $f$ by itself. $\begin{aligned} 0.3&=0.5f-0.7 \\ \\ 0.3{+0.7} &=0.5f-0.7 {+0.7}~~~~~~{\text{add }0.7} \text{ to each side}\\ \\ 0.3{+0.7}&=0.5f-\cancel{ 0.7} {{+}\cancel{{0.7}}}\\ \\ 0.3{+0.7}&=0.5f \end{aligned}$ $\begin{aligned}1&= 0.5f \\ \\ \dfrac{1}{{0.5}} &= \dfrac{0.5f}{{0.5}} ~~~~~~~\text{divide each side by } {0.5} \text{ to get } f \text{ by itself }\\ \\ \dfrac{1}{{0.5}} &= \dfrac{\cancel{0.5}f}{\cancel{{0.5}}} \\ \\ \dfrac{1}{{0.5}}&= f \end{aligned}$ The answer: $f={2}$ Let's check to make sure. $\begin{aligned} 0.3&=0.5f-0.7 \\\\ 0.3&\stackrel{?}{=} 0.5\left({2}\right)-0.7 \\\\ 0.3&\stackrel{?}{=} 1-0.7 \\\\ 0.3 &= 0.3 ~~~~~~~~~~\text{Yes!} \end{aligned}$